Overrunning clutches, sometimes referred to as roller clutches or one-way brakes, find many applications in automotive vehicles. Typically, an overrunning clutch operates in an annular space between relatively rotatable inner and outer clutch races. A plurality of wedging elements, most often cylindrical rollers, are retained by a clutch cage installed within the annular space. In most applications, an overrunning clutch will operate in an environment where there is no need to provide any kind of seal to confine a lubricant within the annular space, as is typically done for a bearing.
However, there is one automotive application for an overrunning clutch that requires a structure to confine a lubricant to or within the annular space between clutch races. A typical vehicle automatic transmission includes a multi-plate fluid operated friction clutch, not to be confused with the overrunning clutch. The friction clutch generally includes a plurality of interleaved friction disks and steel plates which surround the outer race of the overrunning clutch. The inner or cam race is journaled on the transmission shaft, and forms an annular space with the outer race. A cage, which retains a plurality of cylindrical rollers, is installed in the annular space between the races. The overrunning clutch acts as a shift timer to improve the smoothness of the transmission's shifting. This location of the overrunning clutch saves axial space but also presents a problem. When the disks and plates of the frictin clutch are disengaged, they rotate very rapidly relative to one another with a very small clearance. Without a lubricant between them, a great deal of heat and wear would be generated. Therefore, the transmission must continually supply lubricant between the disks and steel plates when the friction clutch is disengaged, which is generally supplied from a port in the transmission shaft. Because the overrunning clutch is, in effect, in the way, that lubricant must go radially outwardly through it. After exiting the shaft, the lubricant is directed radially outwardly through a port in the inner race, through the annular space between the races, and finally out through a port in the outer race and finally to the disks and plates. The force with which this lubricant is outwardly directed is primarily centrifugal and dependent on the speed of rotation of the outer race, which may be quite high. Seeking the path of least resistance, this lubricant will attempt to exit axially through the sides of the annular space between the races. Unless that annular space is somehow blocked, adequate lubricant may not reach the friction clutch.
Confining the lubricant presents unique problems in the context of the overrunning clutch, problems not found in the context of a rolling element bearing. While a bearing also includes inner and outer annularly spaced races, the operation of a bearing is quite different. In a bearing, the rolling elements are very closely confined between annularly spaced pathways on the inner and outer races. Consequently, it is simple to maintain the bearing races very closely coaxial to one another. With a typical overrunning clutch, however, the clutch races can not be so easily maintained in close coaxial relation, at least without the use of separate bearings, which is undesirable for cost and space reasons. A typical overrunning clutch maintains the clutch races coaxial with cage journal blocks, not with a separate bearing. Such a clutch is generally referred to as a concentric control clutch. The journal blocks fit closely within and maintain the annular space between the clutch races, thereby keeping the clutch races substantially coaxial. The journal block fit is purposely designed to have a certain amount of tolerance or looseness, however, significantly greater than the tolerance with which rolling bearing elements fit between bearing race pathways. This is deliberately done to ease the installation of the case assembly between the clutch races, which involves pushing the cage assembly into the annular space. A running eccentricty of the outer race occurs because of the deliberate tolerance in the journal block fit. In the environment of a high speed automatic transmission, the running eccentricity can cause the annular space between the clutch races to change size thousands of times a minute.
The running eccentricity makes it impractical, if not impossible, to apply typical bearing seal technology to the problem of confining a lubricant between the clutch races. A convention bearing seal includes some type of support, such as a snap shield, attached to one bearing race with an elastomer seal lip that rubs on the other race. While a conventional rubbing seal works well with a bearing, since the races are held very closely coaxial, such a seal in an overrunning clutch would experience an increase in friction with every cycle of the running eccentricity, and could be rubbed away. Therefore, current overrunning clutches used in such an environment settle for a labyrinth seal, which are very low friction, but which, of course, cannot provide the complete confinement of the lubricant that a rubbing seal would provide. It would be desirable, if possible, to provide a means that more completely blocked the loss the lubricant out of the annular space that does a labyrinth seal, but without the high friction of a conventional rubbing seal, especially for application in a vehicle automatic transmission.